Treating oxid of zinc.



F. P. DEWEY.

TREATING OXID 0F ZINC.

APPLIUATION'IILBD JUNE 8, 1898.

Patented 001;; 6,1908.

OOOC

' -monly spoken of as low FREDERIG PIDEWEY, OF WASHINGTON, DISTRICT 'OFCOLUMBIA.

A TREATIN oxn) or zmo.

' Specification 61 Letters Patent.

Application filed June a, 1898. Serial No. 682,910. I

To all whom it may concern: I 3e' it known that I, Fnnnnmo P. DEWEYcitizen of the United States, residing at Washington,- in the Districtof Columbia,

have invented 'certainnew and useful Im-' provements in Treating Oxid ofZinc; and I do hereby declare thefollowing-to be a full,

clear, and exact description of the invention,

such as will enable others skilled in the art to which it appertainstomake and use the' same. I

' My invention relates primarily to the conversion of oxid" of zinc intosulfite of zinc, and more particularly to the treatment of the mixtureof galena, pyrite and blende'carrymg a small amount of silver, which iscomgrade sulfid ore. Enormous quantities of these ores are known toexist in various parts of our mining country, particularly at'Leadville, Colorado, which are now practically valueless. They carryfrom 10 to 20 per cent. lead, 'to 25 per cent. iron, to 35 ,per cent.zinc and 10 to ounces silver per ton, together with due containin smallamounts of other things. Smelting charges upon ores carryingzinc arevery high, and it does not pay to smelt them. Various special processeshave .been proposed for then treatment, but noneof them have beensuccessful so far. Among the processes proposed are several in which theore' isroasted and then treated with the sulfurous acid given off in theroasting, inorder to convert the zinc into sulfite, which is dissolved1n water, and separated from the resi- I I I the lead, iron and silver.Brom 3. 'CI'1t1C-a quantitative examination of the venous sulfiteprocesses I have discovered that they are all very seriously handicappedby the enormous-quantities of water that must be handledin order todissolve't-he zinc.

It is .the special object of 'my' invention to br'mgthe zinc of theroasted ore into solution in a minimum quantity'of water, and this Isecure ,by'the use of a very large amount of sulfurous acid applied inav particular manner. The very best result that can be obtained by theprocesses heretofore proposed requires twenty-five tons of .watertodissolve one ton of oxid of zinc while some of" them require as much asone hundred tonsv of water to dissolve one ton of oxid offzinc while bymy process I can dissolveone ton of oxid of zinc in le'ssthan ten tonsof water.-

- In other words while the oldenprocesses can I this source.-

not-yield a solution carrying more than four per cent. of,ox idof' zincmy process yields solutlons carrying over ten .per cent. of oxid ofzinc. Incidentally I also recover my zinc in the form of an oxid ofzincsuitable for smelting to spelterwithout the extraneous reagents.

I have discovered that the amount of oxid of zinc ield in solution by.sulfurous acid water depends upon the amount of sulfurous acid resentin. excess of the quantity required to convert the oxid of zinc intosulfite, and that the ores under consideration do not yield suificientsulfurous acid on being roasted to make-a concentrated solution, sothat,

use of any Patented Oct. 6, 190s.

in order to get such concentrated solutions,

it is necessary to have more, sulfurous acid than the roastin of the oreitself will furnish. I obtain t is extra supply of sulfurous acidpreferably by thesubsequent manipulation of the solution of sulfite ofzinc and thedecomposition of the zinc sulfite itself so that I use mysulfurous acid over and over again, and thus have an abundant supply ofsulfurous acid and a continuous process. Where large quantities of othersulfid ores are being roasted the extrasulfurous acid required maysometimes be obtained from Such concentrated solutions of sulfite ofzinc in sulfurous acid water as I obtain will deposit crystals ofsulfite of zinc on being deprlved of their excess of free sul-I furousacid] This may be accomplishedby the heating of the solution, or bymeans ofa new charge of roasted ore it may be used many times over. Thesolution deprived of its excess ofsulfurousacid as will still containsome'zinc, and, in or er not to waste this, the liquid is cooled whennecessary, and is then recharged withsulfurous acid and used in treatinga fresh lot of ore so as to saturate it again'with zinc. I have alsodiscovered that in dissolving oxid of; zinc in sulfurous acid water itis much easier to keep the zinc dissolved in a small volume of water Ithan it is to dissolvealready formed sulfite of zinc in the same amountof water, so that I prefer to operate in such away that there dissolvingoperation, and this I secure by vacuum, or both'thes'e means combined,and by passing the'evolved sulfurous acid into a isno separationofsulfite of zinc during the I I always having an excess 'of'freesulfurousacid resent in-thesolution. Thisis secured by a ding; theroasted ore to the sulfurous acid waterin small-portions at a time.Furwith watersaturated with sulfurous acid gas, a point is reached whenthe further addition of roasted ore will produce a precipitation ofthe'already dissolved sulfite of zinc, and it is impossible to obtain aconcentrated solu- 1' tion, so that a farther part of my inventionconsists in supplying sulfurous acid gas to the solution while the zincis being dissolved.

The crystals obtained by depriving the concentrated solution of zinc insulfurous 1 acid water of its free sulfurous acid consist of sulfite ofzinc, andon heating these crystals for a short time to about 1000 0.they are completely decomposed and yield a very pure oxid of zinc whichis eminently fitted for spelter smelting. Repeated trials have producedan oxid practically free from sulfur, showing less than 0.01 per cent.of that element. By my process the zinc is removed from the ores, andrecovered in a valuable form, while the silver, lead and iron are leftin a residue that smelts easily, and yields base bullion. I i

. To more fully set out my invention I will describe it as applied to aparticular ore w without limiting myself to the details. The ore,carrying 20 ounces silver per ton, 10 per cent. 'lead, per cent. zincand 2 per cent. silica, the balance being mainly iron and sulfur, isfirst roasted, preferably until the 11011 is converted into sesquioxid.The sul furous acid given off during the roasting is conveyed to asuitable scrubber where it is absorbed in water. The roasted ore is thenplaced in a ho per or bin from which it is automatically ed in smallportions at a time into a vat or tub containing an aqueous solut on ofsulfurous acid, preferably the solutron obtained by absorbing thesulfurous acid glven off in roasting the ore, at the same time I moresulfurous acid is conducted into the 'SOllltlOIl, preferably thatobtained in the next step ofthe process. The feeding of the roasted oreand the introduction of the sulfurous acid gas are so regulated that thefree sulfurous acid is always in excess. When a sufiiciently strongsolution of zinc is obtained the contents of the vat are removed to afilter where the solution is separated from the res1due. The residue issuitably washed and smelted for the silver and lead 1t contains, or itis otherwise utilized. The solution of sulfite of zinc in sulfurous acidwater is next transferred to a closed vessel provided with su tableoutlets where it is gently heated to drive off the sulfurous acid gas,atthe same time a suction pump aids the evolution of gas ,and drives theevolved 'gas into a fr sh lot of sulfurous acid has been sufiicientlyremoved the crystals of sulfite of zinc are separated from.the l1qu1d,which goes'to the scrubber ito be charged with sulfurous acid gas and be'=used again inthedissolving vat.

{fore in the dissolving vat. When the freetion, partly in section, ofthe application of the process.

.A represents an ordinary reverberatory furnace for the roasting ofores.

C represents a suction fan, which gathers up sulfurous acid from varioussources and delivers it, through the pipe D, which is provided withvarious openings at its terminus, into the vat E. The vat E has an inletF provided with a hop er and feeding a paratus, not shown, drintroducing tie roasted ore gradually into the vat E. also a dischargeG, for the removal of the residue remaining after treating the roastedore with sulfurous acid together with the ,solution of sulfite of zincproduced.

N is an outlet for any excess of gas introduced into the vat E.

H represents a vat, in which the solution of sulfite of zinc is heatedby the steam coil K in order to drive off sulfurous' acid. It isprovided with an inlet I for introducing the solution, an outlet L forwithdrawin the precipitated sulfite of zinc, and an out et M or theremoval of the sulfurous acid liberated by the heat. I

N represents a closed retort, sultably placed within a heating furnace,not shown, in which the sulfite of zinc is heated,in order to decomposeit, with the evolution of sulfurous acid, which is Withdrawn from theretort by the pipe M.

' M M represent a series of gas ways, provided with suitable valves, notshown, whlch serve to conduct the sulfurous acid developed it va'iousstages in the process to the suction B represents-a flue provided with adamper, not shown, for conveyin the roasting gases to the chimney when tese gases are not required in the operation of the process.

As previously pointed out it is essential to the successful extractionof zinc from its ores by the use of sulfurous acid that when the sulfiteof zinc is formed there should be It has .suflicient extra sulfurousacid present in the explains why all sulfurous acid leaching processesare so inefficient on zinc ores, for, in the early stages oftheleaching, the sulfurprecipitated back into the ore so that finally-the' first leach solution running from the charge' is practically'freefrom zinc and a very large amount of solution is required I ceases -ousacid "of the leachfliq'uor is gradually neutralized bythe zinc andsulfiteof zinc is subsequently to re-dissolve .the precipitated sulfiteof zinc out of the ore. The actual amount of. this extra sulfurous'a'cid required variesin difierent cases. It depends ,upon the amount ofzinc dissolved. and increases with the amount of zinc held in solution.Inthe claims this extra sulfurous acid required to holdthe zinc sulfitein solu-' f at a time to water containing su'lfurous acid so that thefree sulfurous acid remains ing sulfurous acid, and simultaneouslysupplying sulfurous acidto the solution so that the free sulfurous acidis always. in excess, substantially as described. r

3. The process of separating oxid of zinc from oxids insoluble insulfurous acid water,

which consists'in adding the mixed oxids to water containing sulfurousacid, siniultaneously, supplying sulfurous acid to the solution so thatthe free sulfurous acid is always in excess, and-separating the solutionfrom.

the residue, substantially as described.

4. The process' of' 'treating sulfids con taining zinc, which consistsin subjecting the sulfids to an oxidizing. roast and graduallyintroducing the roasted ore into'water containing sulfurous acid .sothat the free sulfurous acid remains always in excess, sub- .stantiallyas described. n l

5.. The process of treating sulfids containmg zmc, which, consists insubjectin the sulfids to an oxidizingroast, gradual y introducing the.roasted ore into water con- I taining sulfurousacid, and at the sametime supplying fresh s'ulfurous acid to the solutlon so that the freesulfurous acid is always in excess, substantially as described.

6. The process 'of treating sulfids containing zinc, which consists insubjectin the sul fids to an oxidizing roast, gradua ly' introducmg theroasted ore into Water containing sulfurous acid, and at the same timesupplymg fresh sulfurous acid to the solution so that the free sulfurousacid is alwa .s in ex-' cess, and separating the solution rom theresidue, substantially'as described.

7. The process of. treating mixed sulfids of zinc, lead and iron,-whic hconsists-in subjecting' the sulfids to an oxidizing roast,

gradually introducin the roasted ore into water containing sul urousacid, and at the same time supplying fresh sulfurous acid to thesolution, substantially as described. I

8. The rocess of treating mixed sulfids of zinc, lea and iron, whichconsists in subjecting' the sulfids to an oxidizing roast,

gradually introducin the roasted ore into water containing sulfiirousacid, and at the same time supplying fresh sulfurous acid to thesolution, and separating the solution from the insoluble residue,substantially as described.

9. The process of treating mixed sulfids of tiallyas described. alwaysin excess, substantially as described. 2. The process of dissolving oxidof zinc, which consists in adding it to water contain:

10. The process of treating mixed sulfids of zinc, lead and ironcontaunngsilver,

, which'consists in subjecting the sulfids to an oxidizing roast,gradually introducing the roasted ore into Watercontaining sulfurousacid, and at the same time supplying fresh sulfurous acid to thesolution, separating the solution from the insoluble residue, andsmeltin the residue to extract the silver and lead, su stantially asdescribed. I

11. The process of treating mixed sulfids of. zinc," lead and ironcontainin silver, which consists in subjecting the sul ds to anoxidizing roast, gradually introducing the roasted ore into watercontainin sulfurous acid, andat the same time supp ying fresh.

sulfurous acid to the solution, separating the solution from theinsoluble residue, recovering the zinc sufite from the solution and 5smeltin the residue to extract the silver and lead, 'su stantially asdescribed. V

12. In the treatment of ores the process which consists in subjectingthe oxidized ores to the'actioniof an aqueous solutlon of sulfurous acidcontaining an excess of free sulfurous' acid, separating the solutlon ofsulfite thus formed from the balance of the ore, driving off the excessof free sulfurous acid'and reabsorbing it in water in the treatment of afresh charge of ore; substantially as described.

'13. In the treatment'of ores the process which consists in subjectingthe oxidized oresto'theactionfof an aqueous solution of sulfurous acidcontaining an excess of free sulfurous acid, separatlng the solut1on ofsulfite thus formed fromthe balance of the ore, driving off the excessof free sulfurous acid and precipitating the dissolved sulfite,

absorbing the sulfurous acid thereby developed in water in the treatmentof a fresh charge of ore; substantially as described.

14. In the treatment of ores the, continu ous rocess which consists insubjecting the oxidized ores to the action of an aqueous solution ofsulfurous acid containing an excess of free sulfurous acid, separatingthe solution of sulfite thus formed from the balance of the ore, drivingoff the excess of free sul furous acid and precipitating the dissolvedsulfite, separating the precipitated sulfite from the liquid andrecharging the liquid with sulfurous acid in the treatment of a freshcharge of ore; substantially as described.

'15. In the treatment of mixed sulfids of zinc, lead and iron, theprocess, which consists in subjecting the sulfids to an oxidizing roast,converting the oxid of zinc thus formed into sulfite of zinc bycombining it with sulfurous acid,separating the sulfite of zinc from thebalance of the ore, decomposing f1the sulfite of zinc and reabsorbingthe en in the treatment of a fresh lot of roasted sulfids; substantiallyas described.

16. In the treatment of mixed sulfids of zinc, lead and iron, theprocess, which consists in subjecting the sulfids to an oxidizing roast,adding the oxidized ore to an aqueous solutionof sulfurous acidcontaining an excess of free sulfurous acid, separat= '"rous acidthereby developed in Water ing the solution of sulfite of zinc thusformed from the balance of the ore, driving off the excess of freesulfurous acid from the solution and reabsorbin the sulfurous aciddriven off in water 1n the treatment of a fresh lot of roasted sulfids;substantially as described.

17 .In the treatment of mixed sulfids of zinc, lead and iron, thecontinuous process, which consists in subjecting the sulfids to anoxidizing roast, adding the oxidized ore to an aqueous solution ofsulfurous acid con taining an excess of free sulfurous acid, separatingthe solution of sulfite of zinc thus formed from the balance of the ore,driving off the excess of free sulfurous acid from the solution andprecipitating the dissolved sul fite of zinc, separating theprecipitated sulfite of zinc from the liquid and recharging the liquidWith sulfurous acid in the treatment of a fresh charge of ore;substantially as described.

18. In the extraction of zinc from its oxidized ores the step whichconsists in driving sulfurous acid into a charge of ore and solu tionand thereby agitating the ore in the solution substantially asdescribed.

In Witness whereof, I have hereunto set my hand in the presence of twowitnesses,

FREDERIC P. DEWEY. Witnesses f HORACE A. Doses, JULIA M. Perm.

